1. Field of the Invention
The present invention relates to a thermal type ink jet head for ejecting an ink drop from an ink jet nozzle (ink ejecting nozzle) onto a recording medium by using a heat generating heater and an ink jet printer using the ink jet head.
2. Description of the Related Art
In the case where an ink jet head of a thermal type ink jet printer is of, for example, a top shooter type for ejecting an ink liquid drop substantially in a perpendicular direction to a head substrate, the ink jet head has a thin film resistor formed on a semiconductor substrate such as a silicon substrate that is a head substrate, an ink jet nozzle provided substantially above this thin film resistor, and an ink flow passage formed through a partitioning wall layer on the semiconductor substrate in communication with this ink jet nozzle, thereby rapidly boiling a part of the ink within the ink flow passage and generating bubbles to eject the ink liquid drop substantially in the perpendicular direction to the substrate from the ink jet nozzle.
It is desired that a diameter of the ink jet nozzles is reduced and the ink jet nozzles are arranged in higher density so that an image of high quality may be printed on a recording paper at a higher resolving power. On the other hand, it is desired that a longitudinal head in which the ink jet nozzles are arranged on a large scale, i.e., a line head in which the ink jet nozzles are arranged at full width length of the recording paper of, for example, A4 size, is developed so that the print with a high quality and the higher resolving power may be outputted for a short period of time.
In this case, it is general to use a silicon substrate as the substrate in view of the easiness of the manufacture of the ink jet head in order to form the heat generating heaters in one-to-one relation with the ink jet nozzles on the substrate. However, since the ink jet head produced by the silicon substrate is cut and manufactured from the silicon wafer having a predetermined size such as a six-inch size or the like, an expensive silicon wafer having a large size has to be used for manufacturing the longitudinal head. Furthermore, since the longitudinal head length is also limited by the size of the silicon wafer, it is impossible to make the above-described line head from a single substrate in a one-chip manner, and in addition it is impossible to manufacture the line head at low cost.
On the other hand, it is conceivable to manufacture an ink let head by using a glass substrate that is relatively less costly and freer in size than the silicon substrate that is thus costly and not free in size.
For instance, in JP 2001-191529A, there is disclosed an ink jet head having a structure of a heat sink layer having a thickness of 1 to 2 μm and a high thermal conductivity which is made of a metal such as aluminum, copper and gold on top of a soda lime glass substrate; an insulating layer on top thereof; a heat generating heater composed of a resistor layer and a conductive layer on top thereof; and a protective layer on top thereof.
In this case, since the metal heat sink layer is located below the heat generating heater layer, it is considered to have a function for rapidly diffusing thermal energy generated from the heat generating heater and opening the heat.
However, in such a head structure, when the density of the ink jet nozzles is increased, for example, the density of the ink jet nozzle is increased to 600 npi (nozzle/inch) or more, the heat generating heaters are integrated at a high density. Further, when the ink liquid drop is ejected at an ink jet (ejecting) cycle corresponding to 10 kHz or more, the case is widely found out in which the release of the heat generated in the heat generating heater cannot catch up with the heat generation so that the temperature around the heat generating heater is elevated and the continuous let of the ink liquid drop becomes impossible.
Since the thermal conductivity of the metal heat sink layer is extremely high, it is impossible to use material having higher thermal conductivity than that.